In conventional pressure transducers of the flexure type, a pressure difference is applied by introducing fluid, gas or other pressure media at a pressure to be measured via a port capped by the flexure and maintaining a known pressure, for example a vacuum, to the other side of the flexure. Typically, strain gauges are placed on the reference side of the flexure. This structure results in two pressure chambers on each side of the flexure, one of which being the reference chamber and the other being exposed to the pressure to be measured. In order to provide a useful gauge, strain gauge connections must be brought through the reference chamber.
The provision of leads connecting the strain gauges and penetrating the reference chamber casing presents a considerable problem in the construction of a pressure sensor of the flexure type. In order to counter the effects of shock and vibration, to which transducers of this type are often subjected, stiff wire is desirable. However this requirement is in conflict with the fundamental operation of the sensor which is based upon movement of the flexure member upon which the strain gauges are mounted. The stiff wires mechanically "load" or dampen the response of the flexure member to pressure changes. A known solution to this problem is to provide a terminal carrying member proximate the strain gauges, bearing terminal pads to which connection may be made with comparatively flexible wire, for example gold wire, and other terminal pads to which connection may be made with comparatively rigid wire, for example nickel, to conduct the connection out through the reference chamber casing.
Pressure transducers of the flexure type are typically formed of metallic components, for example stainless steel, welded together for ruggedness. The provision of terminal pads for such transducers presents a considerable problem since they must be both proximate the flexure and individually electrically isolated from the metallic parts. One solution to this problem is to provide terminal pads upon an insulating substrate, such as a glass-fiber/epoxy board, formed as an annulus and mounted co-axially with the flexure so that the more flexible connections may be led from the flexure through the center of the substrate and the more rigid connections away from its periphery.
In such a design of a flexure type pressure transducer the problem of fixing the substrate proximate the flexure is encountered. Because of the nature of the materials involved the preferred fixing method of welding is of course unavailable. One fixing method in common usage is that of adhesive bonding. Unfortunately the bonding of a component in the region of a flexure, for example with epoxy resin, has the attendant dangers of excess resin contacting the flexure and disrupting its performance. This is in addition to other disadvantages of bonding components including difficulty and expense of assembly, uncertainty as to adhesion quality and poor mechanical strength.